The present invention relates to a structure for providing relative positioning of a rotary shaft of a rotary detecting device such as a rotary encoder or a rotary switch, and a rotary shaft.
FIG. 6 is a cross-sectional view of an example of such a structure in the prior art. A frame 3 is positioned above a rotary shaft 2, and the rotary shaft 2 is provided with a joint unit 1, for example, a collet chuck. A pressing clamp 5 is provided for holding and clamping the rotary detecting device 4 to the frame 3. Frame 3 has a hole 6 aligned concentrically with said rotary shaft 2, and by inserting projecting portion 7 of said rotary detecting device 4 into hole 6, the rotary detecting shaft 8 can be aligned with the rotary shaft 2. The rotary detecting shaft 8 is passed through hole 6, extends downward, and is connected to said rotary shaft 2 by joint unit 1.
FIG. 7 is a cross-sectional view for illustrating further prior art. Frame 3 is provided with a hole 11 for the passage of the rotary detecting shaft 8 and screw holes 12 for fixing the rotary detecting device 4 to the frame 3. Further, frame 3 is positioned above the rotary shaft 2 such that hole 11 is above said rotary shaft 2. The rotary detecting device 4 is fastened to frame 3 by inserting the rotary detecting shaft 8 through hole 11 so that the front end portion of rotary detecting shaft 8 can be connected to said joint unit 1. Then the screws 13 are tightened into said screw holes 12.
Looking back to FIG. 6, the rotary detecting shaft 8 is aligned with rotary shaft 2 by inserting the projecting portion 7 of the rotary detecting device 4 into hole 6 which is provided on the frame 3. The diameter of hole 6 must be slightly larger than the external diameter of the projecting portion 7 for the setting operation of the rotary detecting device 4 to be efficient and smooth. This loose fitting prevents exact alignment of the rotary detecting shaft 8 and the rotary shaft 2. Therefore, a radial force due to the misalignment of both shafts 2 and 8 is imparted to the rotary detecting shaft 8 which causes damage to the bearings.
The aforementioned disadvantage can be avoided if both shafts 2 and 8 are connected by a suitable joint such as oldham's coupling joint. However, such a coupling joint must be fixed and released, which decreases workability and efficiency. Thus, such a coupling joint cannot be used in a production line.
On the other hand, alignment between rotary detecting shaft 8 and rotary detecting device 2 in the structure shown in FIG. 7 is executed by fixing the rotary detecting shaft 8 to the joint unit 1 before the screws 13 are tightened. Still though, both 2 and 8 may be misaligned after the screws 13 are tightened since aligning the fixed plate 3 with the rotary shaft 2 is difficult. The aforementioned disadvantage remains.
Again, shafts 2 and 8 can be connected by a suitable coupling joint such as oldham's coupling joint. However, such a coupling joint changes the rotational angle between the rotary shaft 2 and rotary detecting shaft 8 which decreases the accuracy of the detection.